Herpes simplex virus ICP4 as an inhibitor of apoptosis

ABSTRACT

The ICP4 protein of herpes simplex virus plays an important role in the transactivation of viral genes. The present invention discloses that ICP4 also has the ability to inhibit apoptosis. This function appears to reside in functional domain distinct from the transactivating function, as indicated by studies using temperature sensitive mutants of ICP4 that transactivating function at elevated temperatures. Also disclosed are methods for inhibition of apoptosis using ICP4 or an ICP4 encoding gene, such as an α4 gene, methods of inhibiting ICP4&#39;s apoptosis-inhibiting function, and methods for the production of recombinant proteins and treatment of HSV infections.

The government may own certain rights in this application by virtue of federal funding under grant numbers Al124009 (NIAID) and CA47451 (NCI).

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates to the fields of molecular and cell biology generally, and more specifically, it addresses mechanisms for growth control in eurkaryotic cells. In particular, there are provided viral genes that inhibit normal cell death and methods for use thereof.

II. Related Art

The control of host cell gene expression, and often the control of genes involved in DNA replication, are integral parts of the life cycle of a virus. However, recent evidence suggests that most eukaryotic cells respond to viral disruption of normal cellular physiology by undergoing programmed cell death (apoptosis) (White, 1993). To counteract this, many viruses have evolved mechanisms to block host cell death (Clem and Miller, 1994; White and Gooding, 1994). In several cases, viral genomes have been found to contain genes whose products interact with proteins that play a central role in regulating cell survival.

Programmed cell death is triggered by several factors and may take various forms. For example, the synthesis of double-stranded RNA activates kinases which phosphorylate the α subunit of eIF-2 and completely turn off protein synthesis (Sarrel, 1989). Ultimately, activation of metabolic pathways causes a pattern of morphological, biochemical, and molecular changes which result in cell death without spillage of cellular constituents which would result in an inflammatory response detrimental to the host (Wyllie, et al.).

Apoptotic cell death is commonly observed during embryogenesis and organ involution and in the natural death of terminally differentiated cells at the end of their life span. Most viruses which induce either the shut-off of protein synthesis or apoptosis also have evolved mechanisms which block host responses and enable them to replicate in their hosts (Shen and Shenk, 1995). Among the best-known examples of viral gene products which block apoptosis are the adenovirus EIB M_(r) 19,000 protein (Rao, et al, 1992.), vaccinia CrmA protein (Ray, et al.), simian virus 40 (SV40) T antigen (McCarthy, et al., 1994), human papillomavirus No. 16 (HPV 16) E6 protein (Pan and Griep, 1994), Epstein-Barr virus BHRF1 protein (Henderson, et al., 1993) and human cytomegalovirus IE1 and IE2 gene products (Zhu, et al., 1995). Herpes simplex virus 1 (HSV-1) encodes a protein, .sub.γ1 34.5, which blocks the phosphorylation of eIF-2α (Chou and Roizman, 1992).

The utility of proteins that are capable of inhibiting apoptosis are manifold. First, such proteins, or their corresponding genes, may be used to immortalize cell lines that otherwise would perish during culture. This makes possible not only the study of these cells, but also presents the option of growing these cells in large numbers in order to isolate protein species therefrom. Second, the identification of inhibitors of apoptosis and their function permits the possible intervention, in a clinical setting, when these proteins are interfering with normal programmed cell death, or apoptosis. This may be accomplished by providing an inhibitor or an antisense nucleic acid that interferes with the expression of a protein that interferes with apoptosis. Thus, the identification of novel proteins having these activities and uses provide important new tools for those working in this arena.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide methods for the use of infected cell protein number 4, or ICP4, and its cognate gene α4, as inhibitors of apoptosis. In addition, it is an object of the present invention to provide methods for the use of agents that inhibit ICP4 and/or α4 in order to induce apoptosis in HSV infected cells. It also is an object of the present invention to provide methods for the identification of agents that inhibit the apoptosis-inhibiting function of ICP4.

In satisfying these goals, there is provided a method for blocking apoptosis of a cell comprising the step of providing to the cell an HSV ICP4 polypeptide or an HSVα4 gene. The α4 gene may be contained in an expression vector and, further, under the control of a promoter active in eukaryotic cells. One such promoter is the a tetracycline controlled promoter. The expression vector further comprises a selectable marker and/or further comprises a gene encoding a second polypeptide under the transcriptional control of a promoter active in eukaryotic cells.

In another embodiment, there is provided a method for inducing apoptosis in a cell infected with HSV comprising the step of administering to said cell an agent that inhibits HSV ICP4 function in said cell. The agent may inhibit transcription or translation of an HSV α4 gene or transcript or may bind to an HSV ICP4 polypeptide. The reagent may be an antisense HSV α4 construct an antibody that binds immunologically to an HSV ICP4 polypeptide. Particular antisense constructs are oligonucleotides that hybridizes to a 5'-untranslated region for an HSV α4 gene or a translational start site for an HSV α4 transcript. Particular antibodies are polyclonal sera against ICP4 or a monoclonal antibody against ICP4.

In yet another embodiment, there is provided a method for treating a subject with an HSV infection comprising the step of inhibiting HSV ICP4 function. The inhibition may comprise providing to the subject a first pharmaceutical composition comprising an HSV α4 antisense construct or a monoclonal antibody that binds immunologically to an HSV ICP4 polypeptide. The first pharmaceutical composition may be applied topically to HSV infected cells in said patient. The method may further comprise the step of providing to said subject a second pharmaceutical composition comprising a conventional anti-HSV agent, such as acyclovir. Acyclovir is delivered via a route selected from the group consisting of topically, orally and intravenously.

In yet still another embodiment, there is provided a screening method for compounds having inhibitory activity against HSV ICP4 polypeptide-induced inhibition of apoptosis comprising the steps of (a) providing a first cell comprising an HSV α4 gene under the control of an HSV immediate early promoter; (b) infecting said first cell with a herpes simplex virus that lacks a functional α4 gene; (c) contacting said first cell with a test compound; (d) incubating said first cell under conditions permitting viral replication; and (e) comparing the cell pathology of said first cell following incubation with the cell pathology of a second cell that lacks an HSV α4 gene following infection with said herpes simplex virus and the cell pathology of a third cell comprising an HSV α4 gene under the control of an HSV immediate early promoter following infection with said herpes simplex virus but in the absence of said test compound. Cell pathology comprises condensation of chromatin, obliteration of nuclear membranes, vacuolization, cytoplasmic blebbing and DNA fragmentation.

The screening method may employ a cell line which contains an integrated copy of a wild-type HSV α4 gene under the control of an α4 promoter and a herpes simplex virus that lacks a functional HSV α4 gene has a deletion in both copies of the virally-encoded α4 genes. For example, the herpes virus may carry a temperature sensitive mutation in both copies of the virally-encoded α4 gene; incubation is at 39.5° C.

Another screening method for compounds having inhibitory activity against HSV ICP4-induced inhibition of apoptosis comprises the steps of (a) providing a first cell comprising an HSV α4 gene under the control of an inducible promoter; (b) inducing transcription from said promoter; (c) contacting said first cell with a test compound; (d) incubating said first cell under conditions expression of an HSV ICP4 polypeptide; and (e) comparing the cell pathology of said first cell following incubation with the cell pathology of a second cell not having an HSV α4 gene following induction and the cell pathology of a third cell comprising an HSV α4 gene under the control of an inducible promoter following induction but in the absence of said test compound.

Yet another screening method for compounds having inhibitory activity against HSV ICP4 polypeptide-induced inhibition of apoptosis comprises the steps of (a) providing a first cell; (b) infecting said first cell with a herpes simplex virus; (c) contacting said first cell with a test compound; (d) incubating said first cell under conditions permitting viral replication; and (e) comparing the cell pathology of said first cell following incubation with the cell pathology of a second cell treated with said test compound alone and the cell pathology of a third cell following infection with said herpes simplex virus but in the absence of said test compound.

In still yet a further embodiment, there is provided a method for expressing a polypeptide in a cell comprising the steps of (a) contacting a cell with a herpes virus vector encoding said polypeptide; (b) contacting said cell with an agent that blocks the transactivating function of ICP4 but does not block the apoptosis inhibiting function of ICP4.

Other objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein.

FIG. 1: Diagrammatic representation of the HSV-1 genome showing the location of the α4 and U_(L) 29 genes encoding ICP4 and ICP8, respectively. The reiterated sequences (open rectangles) flanking the unique short (U_(S)) and unique long (U_(L)) sequences (thin lines) and the location and direction of genes are as shown. Because the α4 gene maps within inverted repeats flanking the U_(L), it is present in two copies per genome. The hatched lines within the rectangles indicates the position of the sequences deleted from the d120 mutant (DeLuca, et al., 1985).

FIG. 2A-L: Nucleotide and amino acid sequence of α4 and ICP4, respectively.

DETAILED DESCRIPTION OF THE INVENTION

I. Herpes Simplex Virus

Herpes simplex viruses, designated with subtypes 1 and 2, are enveloped viruses that are among the most common infectious agents encountered by humans, infecting millions of human subjects worldwide. These viruses cause a broad spectrum of disease which ranges from relatively insignificant to severe and life-threatening. Clinical outcome of herpes infections is dependent upon early diagnosis and prompt initiation of antiviral therapy. Despite some successful efforts in treating HSV infectious, dermal and epidermal lesion often recur, and HSV infections of neonates and infections of the brain are associated with high morbidity and mortality.

The large, complex, double-stranded DNA genome encodes for dozens of different gene products, some of which derive from spliced transcripts. In addition to virion and envelope structural components, the virus encodes numerous other proteins including a protease, a ribonucleotides reductase, a DNA polymerase, a ssDNA binding protein, a helicase/primase, a DNA dependent ATPase, a dUTPase and others.

HSV genes form several groups whose expression is coordinately regulated and sequentially ordered in a cascade fashion (Honess and Roizman, 1974; Honess and Roizman 1975; Roizman and Sears, 1995). The expression of α genes, the first set of genes to be expressed after infection, is enhanced by the virion protein number 16, or α-transinducing factor (Post et al., 1981; Batterson and Roizman, 1983; Campbell, et al., 1983). The expression of β genes requires functional α gene products, most notably ICP4, which is encoded by the α4 gene (DeLuca et al., 1985). γ genes, a heterogeneous group of genes encoding largely virion structural proteins, require the onset of viral DNA synthesis for optimal expression (Holland et al., 1980).

In line with the complexity of the genome, the life cycle of HSV is quite involved. In addition to the lytic cycle, which results in synthesis of virus particles and, eventually, cell death, the virus has the capability to enter a latent state in which the genome is maintained in neural ganglia until some as of yet undefined signal triggers a recurrence of the lytic cycle.

II. The ICP4 Polypeptide

As stated above, the expression of β genes is regulated in a major fashion by ICP4 (DeLuca et al., 1985), and therefore this gene has a distinct effect on viral DNA synthesis. γ genes, a heterogeneous group of genes encoding largely virion structural proteins, require the onset of viral DNA synthesis for optimal expression (Honess and Roizman, 1975; Holland et al., 1980). ICP4 plays a key role in this process--cells infected with viruses carrying temperature sensitive mutations in the α4 gene and maintained at nonpermissive temperatures express largely α proteins (Dixon and Shaffer, 1980). Furthermore, studies involving shift-up of infected cells from permissive to nonpermissive temperatures have confirmed a key role for ICP4 throughout the viral reproductive cycle.

ICP4 acts both as a transactivator and as a repressor (Roizman and Sears, 1995). The response elements for the repressor functions of ICP4 are high affinity binding sites located in the proximity of transcription initiation sites of the genes repressed by the protein (Kristie and Roizman, 1986a, Kristie and Roizman, 1986b, Faber and Wilcox, 1986, Muller, 1987, Michael and Roizman, 1989, Michael and Roizman, 1993). The strength of repression is dependent on both the distance and stereoaxial alignment with the TATA box (Leopardi et al., 1995, Kuddus et al., 1995). Low affinity sites for binding of ICP4 have also been documented, but their function is less well understood (Kristie and Roizman, 1986a, Kristie and Roizman, 1986b, Michael et al., 1988). The response elements thought to act in the transactivation of viral genes by ICP4 are not known, but mutations in ICP4 may affect repression and activation independently of each other (Shepard and DeLuca, 1991).

According to the present invention, a novel functional aspect of ICP4 previously undisclosed is its ability to inhibit apoptosis. Apoptosis, or programmed cell death, is characterized by certain cellular events, including nuclear condensation, DNA fragmentation, cytoplasmic membrane blebbing and, ultimately, irreversible cell death. Apoptosis is an energy-dependent event. For the purposes of this application, apoptosis will be defined as inducing one or more of these events. Thus, the use of the term "ICP4" in this application encompasses polypeptides having the anti-apoptosis function of ICP4. These need not be wild-type ICP4.

This functional attribute is manifested, for example, in ICP4's ability to protect cells from apoptosis triggered by modification of cellular physiology by other viral genes. This observation permits utilization of ICP4 in a number of ways that could not have been predicted from the prior art. For example, according to the present invention, the production of HSV vectors or recombinant proteins from HSV vectors can be enhanced by increasing the apoptosis inhibiting function of ICP4. When cells are infected with HSV, premature cell death can limit the titer of virus produced or the amount of recombinant protein synthesized. Similarly, ICP4 may prolong the life of the cells expressing human or animal genes introduced into cells by viral vectors in order to correct genetic defect. If the cell can be sustained longer, the titer of the virus stocks and the amount of protein should increase.

ICP4 may be obtained according various standard methodologies that are known to those of skill in the art. For example, antibodies specific for ICP4 may be used in immunoaffinity protocols to isolate ICP4 from infected cells, in particular, from infected cell lysates. Antibodies are advantageously bound to supports, such as columns or beads, and the immobilized antibodies can be used to pull the ICP4 target out of the cell lysate.

Alternatively, expression vectors, rather than viral infections, may be used to generate ICP4. A wide variety of expression vectors may be used, including viral vectors. The structure and use of these vectors is discussed further, below. Such vectors may significantly increase the amount of ICP4 protein in the cells, and may permit less selective purification methods such as size fractionation (chromatography, centrifugation), ion exchange or affinity chromatograph, and even gel purification. Alternatively, the expression vector may be provided directly to target cells, again as discussed further, below.

ICP4, according to the present invention, may advantageously be cleaved into fragments for use in further structural or functional analysis, or in the generation of reagents such as ICP4-related polypeptides and ICP4-specific antibodies. This can be accomplished by treating purified or unpurified ICP4 with a peptidase such as endoproteinase glu-C (Boehringer, Indianapolis, Ind.). Treatment with CNBr is another method by which ICP4 fragments may be produced from natural ICP4. Recombinant techniques also can be used to produce specific fragments of ICP4. Because the transactivating and apoptosis-inhibiting functions of ICP4 appear to reside in distinct domains, the ability to make domain-specific reagents now has significance. For example, the ability to provide an apoptosis-inhibiting ICP4 fragment that does not transactivate viral genes may prove to be effective in extending the life of neurons expressing compensatory or therapeutic genes from a viral vector.

It is expected that changes may be made in the sequence of ICP4 while retaining a molecule having the structure and function of the natural ICP4. For example, certain amino acids may be substituted for other amino acids in a protein structure without appreciable loss of interactive capacity with structures such as, for example, substrate-binding regions. These changes are termed "conservative" in the sense that they preserve the structural and, presumably, required functional qualities of the starting molecule. The importance of ICP4 variants is highlighted by the observation, discussed in the examples, that temperature sensitive (ts) mutants of ICP4 exist that are impaired in their ability to transactivate viral genes at elevated temperatures (above about 39° C.), but retain the apoptosis inhibiting function associated with this polypeptide. Further exploration of this dichotomy should reveal significant information on the regions in which these functions lie. Additional variants of this nature may be screened by any of the functional assays provided in the examples.

It has been shown that the transactivation domain of ICP4 lies between about residues 100 and 200, the DNA-binding domains lies between about residues 300 and 500, the nuclear localization domain lies between about residues 700 and 750 and the transactivation domain lies between about residues 750 and 1298.

Conservative amino acid substitutions are generally based on the relative similarity of the amino acid side-chain substituents, for example, their hydrophobicity, hydrophilicity, charge, size, and the like. An analysis of the size, shape and type of the amino acid side-chain substituents reveals that arginine, lysine and histidine are all positively charged residues; that alanine, glycine and serine are all a similar size; and that phenylalanine, tryptophan and tyrosine all have a generally similar shape. Therefore, based upon these considerations, arginine, lysine and histidine; alanine, glycine and serine; and phenylalanine, tryptophan and tyrosine; are defined herein as equivalent.

In making such changes, the hydropathic index of amino acids also may be considered. Each amino acid has been assigned a hydropathic index on the basis of their hydrophobicity and charge characteristics, these are: isoleucine (+4.5); valine (+4.2); leucine (+3.8); phenylalanine (+2.8); cysteine/cystine (+2.5); methionine (+1.9); alanine (+1.8); glycine (-0.4); threonine (-0.7); serine (-0.8); tryptophan (-0.9); tyrosine (-1.3); proline (-1.6); histidine (-3.2); glutamate (-3.5); glutamine (-3.5); aspartate (-3.5); asparagine (-3.5); lysine (-3.9); and arginine (-4.5).

The importance of the hydropathic amino acid index in conferring interactive biological function on a protein is generally understood in the art (Kyte & Doolittle, 1982). It is known that certain amino acids may be substituted for other amino acids having a similar hydropathic index or score and still retain a similar biological activity. In making changes based upon the hydropathic index, the substitution of amino acids whose hydropathic indices are within ±2 is preferred, those which are within ±1 are particularly preferred, and those within ±0.5 are even more particularly preferred.

It also is understood in the art that the substitution of like amino acids can be made effectively on the basis of hydrophilicity, particularly where the polypeptide created is intended for use in immunological embodiments, as in the present case. U.S. Pat. No. 4,554,101, incorporated herein by reference, states that the greatest local average hydrophilicity of a protein, as governed by the hydrophilicity of its adjacent amino acids, correlates with its immunogenicity and antigenicity, i.e., with a biological property of the protein.

As detailed in U.S. Pat. No. 4,554,101, the following hydrophilicity values have been assigned to amino acid residues: arginine (+3.0); lysine (+3.0); aspartate (+3.0±1); glutamate (+3.0±1); serine (+0.3); asparagine (+0.2); glutamine (+0.2); glycine (0); threonine (-0.4); proline (-0.5±1); alanine (-0.5); histidine (-0.5); cysteine (-1.0); methionine (-1.3); valine (-1.5); leucine (-1.8); isoleucine (-1.8); tyrosine (-2.3); phenylalanine (-2.5); tryptophan (-3.4).

In making changes based upon similar hydrophilicity values, the substitution of amino acids whose hydrophilicity values are within ±2 is preferred, those which are within ±1 are particularly preferred, and those within ±0.5 are even more particularly preferred.

Numerous scientific publications have been devoted to the prediction of secondary structure, and to the identification of epitopes, from analyses of amino acid sequences (Chou & Fasman, 1974a,b; 1978a,b; 1979). Any of these may be used, if desired, to supplement the teachings of Hopp in U.S. Pat. No. 4,554,101. Moreover, computer programs are currently available to assist with predicting antigenic portions and epitopic core regions of proteins. Examples include those programs based upon the Jameson-Wolf analysis (Jameson & Wolf, 1998; Wolf et al., 1988), the program PepPlot® (Brutlag et al., 1990; Weinberger et al., 1985), and other new programs for protein tertiary structure prediction (Fetrow & Bryant, 1993).

Two designations for amino acids are used interchangeably throughout this application, as is common practice in the art. Alanine=Ala (A); Arginine=Arg (R); Aspartate=Asp (D); Asparagine=Asn (N); Cysteine=Cys (C); Glutamate=Glu (E); Glutamine=Gln (Q); Glycine=Gly (G); Histidine=His (H); Isoleucine=Ile (I); Leucine=Leu (L); Lysine=Lys (K); Methionine=Met (M); Phenylalanine=Phe (F); Proline=Pro (P); Serine=Ser (S); Threonine=Thr (T); Tryptophan=Trp (W); Tyrosine=Tyr (Y); Valine=Val (V).

In addition to the peptidyl compounds described herein, the inventors also contemplate that other sterically similar compounds may be formulated to mimic the key portions of the peptide structure, called peptidomimetics. Mimetics are peptide-containing molecules which mimic elements of protein secondary structure. See, for example, Johnson et al. (1993). The underlying rationale behind the use of peptide mimetics is that the peptide backbone of proteins exists chiefly to orient amino acid side chains in such a way as to facilitate molecular interactions, such as those of receptor and ligand.

Successful applications of the peptide mimetic concept have thus far focused on mimetics of β-turns within proteins. Likely β-turn structures within ICP4 can be predicted by computer-based algorithms as discussed above. Once the component amino acids of the turn are determined, mimetics can be constructed to achieve a similar spatial orientation of the essential elements of the amino acid side chains, as discussed in Johnson et al., supra.

III. Nucleic Acids Encoding ICP4

Also contemplated by the present invention are nucleic acids encoding ICP4. The gene for ICP4 has been given the designation of α4. Because of the degeneracy of the genetic code, many other nucleic acids also may encode a given ICP4. For example, four different three-base codons encode the amino acids alanine, glycine, proline, threonine and valine, while six different codons encode arginine, leucine and serine. Only methionine and tryptophan are encoded by a single codon. A table of amino acids and the corresponding codons is presented herein for use in such embodiments.

                  TABLE 1     ______________________________________     Amino Acids          Codons     ______________________________________     Alanine   Ala    A       GCA GCC GCG GCU     Cysteine  Cys    C       UGC UGU     Aspartic acid               Asp    D       GAC GAU     Glutamic acid               Glu    E       GAA GAG     Phenylalanine               Phe    F       UUC UUU     Glycine   Gly    G       GGA GGC GGG GGU     Histidine His    H       CAC CAU     Isoleucine               Ile    I       AUA AUC AUU     Lysine    Lys    K       AAA AAG     Leucine   Leu    L       UUA UUG CUA CUG CUG CUU     Methionine               Met    M       AUG     Asparagine               Asn    N       AAC AAU     Proline   Pro    P       CCA CCC CCG CCU     Glutamine Gln    Q       CAA CAG     Arginine  Arg    R       AGA AGG CGA CGC CGG CGU     Serine    Ser    S       AGC AGU UCA UCC UCG UCU     Threonine Thr    T       ACA ACC ACG ACU     Valine    Val    V       GUA GUC GUG GUU     Tryptophan               Trp    W       UGG     Tyrosine  Tyr    Y       UAC UAU     ______________________________________

In order to generate any nucleic acid encoding ICP4, one need only refer to the preceding codon table. Substitution of the natural codon with any codon encoding the same amino acid will result in a distinct nucleic acid that encodes ICP4. As a practical matter, this can be accomplished by site-directed mutagenesis of an existing α4 gene or de novo chemical synthesis of one or more nucleic acids.

The preceding observations regarding codon selection, site-directed mutagenesis and chemical synthesis apply with equal force to the discussion of substitutional mutants in the section of peptides. Normally, substitutional mutants are generated by site-directed changes in the nucleic acid designed to alter one or more codons of the coding sequence.

In order to express an ICP4 polypeptide, or an antisense α4 transcript, it is necessary to provide an α4 gene in an expression vehicle. The appropriate nucleic acid can be inserted into an expression vector by standard subcloning techniques. For example, an E. coli or baculovirus expression vector is used to produce recombinant polypeptide in vitro. The manipulation of these vectors is well known in the art. In one embodiment, the protein is expressed as a fusion protein with β-gal, allowing rapid affinity purification of the protein. Examples of such fusion protein expression systems are the glutathione S-transferase system (Pharmacia, Piscataway, N.J.), the maltose binding protein system (NEB, Beverley, Mass.), the FLAG system (IBI, New Haven, Conn.), and the 6xHis system (Qiagen, Chatsworth, Calif.).

Some of these fusion systems produce recombinant protein bearing only a small number of additional amino acids, which are unlikely to affect the functional capacity of the recombinant protein. For example, both the FLAG system and the 6x His system add only short sequences, both of which are known to be poorly antigenic and which do not adversely affect folding of the protein to its native conformation. Other fusion systems produce proteins where it is desirable to excise the fusion partner from the desired protein. In another embodiment, the fusion partner is linked to the recombinant protein by a peptide sequence containing a specific recognition sequence for a protease. Examples of suitable sequences are those recognized by the Tobacco Etch Virus protease (Life Technologies, Gaithersburg, Md.) or Factor Xa (New England Biolabs, Beverley, Mass.).

Recombinant bacterial cells, for example E. coli, are grown in any of a number of suitable media, for example LB, and the expression of the recombinant polypeptide induced by adding IPTG to the media or switching incubation to a higher temperature. After culturing the bacteria for a further period of between 2 and 24 hours, the cells are collected by centrifugation and washed to remove residual media. The bacterial cells are then lysed, for example, by disruption in a cell homogenizer and centrifuged to separate the dense inclusion bodies and cell membranes from the soluble cell components. This centrifugation can be performed under conditions whereby the dense inclusion bodies are selectively enriched by incorporation of sugars such as sucrose into the buffer and centrifugation at a selective speed.

If the recombinant protein is expressed in the inclusion bodies, as is the case in many instances, these can be washed in any of several solutions to remove some of the contaminating host proteins, then solubilized in solutions containing high concentrations of urea (e.g 8M) or chaotropic agents such as guanidine hydrochloride in the presence of reducing agents such as β-mercaptoethanol or DTT (dithiothreitol).

Under some circumstances, it may be advantageous to incubate the polypeptide for several hours under conditions suitable for the protein to undergo a refolding process into a conformation which more closely resembles that of the native protein. Such conditions generally include low protein concentrations less than 500 μg/ml, low levels of reducing agent, concentrations of urea less than 2M and often the presence of reagents such as a mixture of reduced and oxidized glutathione which facilitate the interchange of disulphide bonds within the protein molecule.

The refolding process can be monitored, for example, by SDS-PAGE or with antibodies which are specific for the native molecule (which can be obtained from animals vaccinated with the native molecule isolated from parasites). Following refolding, the protein can then be purified further and separated from the refolding mixture by chromatography on any of several supports including ion exchange resins, gel permeation resins or on a variety of affinity columns.

In yet another embodiment, the expression system used is one driven by the baculovirus polyhedron promoter. The gene encoding the protein can be manipulated by standard techniques in order to facilitate cloning into the baculovirus vector. A preferred baculovirus vector is the pBlueBac vector (Invitrogen, Sorrento, Calif.). The vector carrying the α4 gene is transfected into Spodoptera frugiperda (Sf9) cells by standard protocols, and the cells are cultured and processed to produce the recombinant protein.

There also are a variety of eukaryotic vectors that provide a suitable vehicle in which recombinant ICP4 can be produced. HSV itself has been used in tissue culture to express a large number of exogenous genes as well as for high level expression of its endogenous genes. For example, the chicken ovalbumin gene has been expressed from HSV using an α promoter. Herz and Roizman (1983). The lacZ gene also has been expressed under a variety of HSV promoters.

In an alternative embodiment, the α4 nucleic acids employed may actually encode antisense constructs that hybridize, under intracellular conditions, to an α4 nucleic acid. The term "antisense construct" is intended to refer to nucleic acids, preferably oligonucleotides, that are complementary to the base sequences of a target DNA or RNA. Antisense oligonucleotides, when introduced into a target cell, specifically bind to their target nucleic acid and interfere with transcription, RNA processing, transport, translation and/or stability.

Antisense constructs may be designed to bind to the promoter and other control regions, exons, introns or even exon-intron boundaries of a gene. Antisense RNA constructs, or DNA encoding such antisense RNA's, may be employed to inhibit gene transcription or translation or both within a host cell, either in vitro or in vivo, such as within a host animal, including a human subject. Nucleic acid sequences which comprise "complementary nucleotides" are those which are capable of base-pairing according to the standard Watson-Crick complementarity rules. That is, that the larger purines will base pair with the smaller pyrimidines to form combinations of guanine paired with cytosine (G:C) and adenine paired with either thymine (A:T), in the case of DNA, or adenine paired with uracil (A:U) in the case of RNA. Inclusion of less common bases such as inosine, 5-methylcytosine, 6-methyladenine, hypoxanthine and others in hybridizing sequences does not interfere with pairing.

As used herein, the terms "complementary" means nucleic acid sequences that are substantially complementary over their entire length and have very few base mismatches. For example, nucleic acid sequences of fifteen bases in length may be termed complementary when they have a complementary nucleotide at thirteen or fourteen positions with only a single mismatch. Naturally, nucleic acid sequences which are "completely complementary" will be nucleic acid sequences which are entirely complementary throughout their entire length and have no base mismatches.

Other sequences with lower degrees of homology also are contemplated. For example, an antisense construct which has limited regions of high homology, but also contains a nonhomologous region (e.g., a ribozyme) could be designed. These molecules, though having less than 50% homology, would bind to target sequences under appropriate conditions.

While all or part of the α4 gene sequence may be employed in the context of antisense construction, short oligonucleotides are easier to make and increase in vivo accessibility. However, both binding affinity and sequence specificity of an antisense oligonucleotide to its complementary target increases with increasing length. It is contemplated that antisense oligonucleotides of 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100 or more base pairs will be used. One can readily determine whether a given antisense nucleic acid is effective at targeting of the corresponding host cell gene simply by testing the constructs in vitro to determine whether the endogenous gene's function is affected or whether the expression of related genes having complementary sequences is affected.

In certain embodiments, one may wish to employ antisense constructs which include other elements, for example, those which include C-5 propyne pyrimidines. Oligonucleotides which contain C-5 propyne analogues of uridine and cytidine have been shown to bind RNA with high affinity and to be potent antisense inhibitors of gene expression (Wagner et al., 1993).

Throughout this application, the term "expression construct" is meant to include any type of genetic construct containing a nucleic acid coding for a gene product in which part or all of the nucleic acid encoding sequence is capable of being transcribed. The transcript may be translated into a protein, but it need not be. Thus, in certain embodiments, expression includes both transcription of a gene and translation of a RNA into a gene product. In other embodiments, expression only includes transcription of the nucleic acid, for example, to generate antisense constructs.

In preferred embodiments, the nucleic acid is under transcriptional control of a promoter. A "promoter" refers to a DNA sequence recognized by the synthetic machinery of the cell, or introduced synthetic machinery, required to initiate the specific transcription of a gene. The phrase "under transcriptional control" means that the promoter is in the correct location and orientation in relation to the nucleic acid to control RNA polymerase initiation and expression of the gene.

The term promoter will be used here to refer to a group of transcriptional control modules that are clustered around the initiation site for RNA polymerase II. Much of the thinking about how promoters are organized derives from analyses of several viral promoters, including those for the HSV thymidine kinase (tk) and SV40 early transcription units. These studies, augmented by more recent work, have shown that promoters are composed of discrete functional modules, each consisting of approximately 7-20 bp of DNA, and containing one or more recognition sites for transcriptional activator or repressor proteins.

At least one module in each promoter functions to position the start site for RNA synthesis. The best known example of this is the TATA box, but in some promoters lacking a TATA box, such as the promoter for the mammalian terminal deoxynucleotidyl transferase gene and the promoter for the SV40 late genes, a discrete element overlying the start site itself helps to fix the place of initiation.

Additional promoter elements regulate the frequency of transcriptional initiation. Typically, these are located in the region 30-110 bp upstream of the start site, although a number of promoters have recently been shown to contain functional elements downstream of the start site as well. The spacing between promoter elements frequently is flexible, so that promoter function is preserved when elements are inverted or moved relative to one another. In the tk promoter, the spacing between promoter elements can be increased to 50 bp apart before activity begins to decline. Depending on the promoter, it appears that individual elements can function either cooperatively or independently to activate transcription.

The particular promoter that is employed to control the expression of a nucleic acid is not believed to be critical, so long as it is capable of expressing the nucleic acid in the targeted cell. Thus, where a human cell is targeted, it is preferable to position the nucleic acid coding region adjacent to and under the control of a promoter that is capable of being expressed in a human cell. Generally speaking, such a promoter might include either a human or viral promoter. Preferred promoters include those derived from HSV, including the α4 promoter. Another preferred embodiment is the tetracycline controlled promoter.

In various other embodiments, the human cytomegalovirus (CMV) immediate early gene promoter, the SV40 early promoter and the Rous sarcoma virus long terminal repeat can be used to obtain high-level expression of transgenes. The use of other viral or mammalian cellular or bacterial phage promoters which are well-known in the art to achieve expression of a transgene is contemplated as well, provided that the levels of expression are sufficient for a given purpose. Tables 2 and 3 list several elements/promoters which may be employed, in the context of the present invention, to regulate the expression of a transgene. This list is not intended to be exhaustive of all the possible elements involved in the promotion of transgene expression but, merely, to be exemplary thereof.

Enhancers were originally detected as genetic elements that increased transcription from a promoter located at a distant position on the same molecule of DNA. This ability to act over a large distance had little precedent in classic studies of prokaryotic transcriptional regulation. Subsequent work showed that regions of DNA with enhancer activity are organized much like promoters. That is, they are composed of many individual elements, each of which binds to one or more transcriptional proteins.

The basic distinction between enhancers and promoters is operational. An enhancer region as a whole must be able to stimulate transcription at a distance; this need not be true of a promoter region or its component elements. On the other hand, a promoter must have one or more elements that direct initiation of RNA synthesis at a particular site and in a particular orientation, whereas enhancers lack these specificities. Promoters and enhancers are often overlapping and contiguous, often seeming to have a very similar modular organization.

Additionally any promoter/enhancer combination (as per the Eukaryotic Promoter Data Base EPDB) could also be used to drive expression of a transgene. Use of a T3, T7 or SP6 cytoplasmic expression system is another possible embodiment. Eukaryotic cells can support cytoplasmic transcription from certain bacterial promoters if the appropriate bacterial polymerase is provided, either as part of the delivery complex or as an additional genetic expression construct.

                  TABLE 2     ______________________________________     PROMOTER     ______________________________________     Immunoglobulin Heavy Chain     Immunoglobulin Light Chain     T-Cell Receptor     HLA DQ α and DQ β     β-Interferon     Interleukin-2     Interleukin-2 Receptor     MHC Class II 5     MHC Class II HLA-DRα     β-Actin     Muscle Creatine Kinase     Prealbumin (Transthyretin)     Elastase I     Metallothionein     Collagenase     Albumin Gene     α-Fetoprotein     τ-Globin     β-Globin     c-fos     c-HA-ras     Insulin     Neural Cell Adhesion Molecule (NCAM)     α.sub.1-Antitrypsin     H2B (TH2B) Histone     Mouse or Type I Collagen     Glucose-Regulated Proteins (GRP94 and GRP78)     Rat Growth Hormone     Human Serum Amyloid A (SAA)     Troponin I (TN I)     Platelet-Derived Growth Factor     Duchenne Muscular Dystrophy     SV40     Polyoma     Retroviruses     Papilloma Virus     Hepatitis B Virus     Human Immunodeficiency Virus     Cytomegalovirus     Gibbon Ape Leukemia Virus     ______________________________________

                  TABLE 3     ______________________________________     Element          Inducer     ______________________________________     MT II            Phorbol Ester (TPA)                      Heavy metals     MMTV (mouse mammary tumor                      Glucocorticoids     virus)     β-Interferon                      poly(rI)X                      poly(rc)     Adenovirus 5 E2  Ela     c-jun            Phorbol Ester (TPA), H.sub.2 O.sub.2     Collagenase      Phorbol Ester (TPA)     Stromelysin      Phorbol Ester (TPA), IL-1     SV40             Phorbol Ester (TPA)     Murine MX Gene   Interferon, Newcastle Disease Virus     GRP78 Gene       A23187     α-2-Macroglobulin                      IL-6     Vimentin         Serum     MHC Class I Gene H-2kB                      Interferon     HSP70            Ela, SV40 Large T Antigen     Proliferin       Phorbol Ester-TPA     Tumor Necrosis Factor                      FMA     Thyroid Stimulating Hormone α                      Thyroid Hormone     Gene     ______________________________________

Use of the baculovirus system will involve high level expression from the powerful polyhedron promoter.

One will typically include a polyadenylation signal to effect proper polyadenylation of the transcript. The nature of the polyadenylation signal is not believed to be crucial to the successful practice of the invention, and any such sequence may be employed. Preferred embodiments include the SV40 polyadenylation signal and the bovine growth hormone polyadenylation signal, convenient and known to function well in various target cells. Also contemplated as an element of the expression cassette is a terminator. These elements can serve to enhance message levels and to minimize read through from the cassette into other sequences.

A specific initiation signal also may be required for efficient translation of coding sequences. These signals include the ATG initiation codon and adjacent sequences. Exogenous translational control signals, including the ATG initiation codon, may need to be provided. One of ordinary skill in the art would readily be capable of determining this and providing the necessary signals. It is well known that the initiation codon must be "in-frame" with the reading frame of the desired coding sequence to ensure translation of the entire insert. The exogenous translational control signals and initiation codons can be either natural or synthetic. The efficiency of expression may be enhanced by the inclusion of appropriate transcription enhancer elements (Bittner et al., 1987).

In various embodiments of the invention, the expression construct may comprise a virus or engineered construct derived from a viral genome. The ability of certain viruses to enter cells via receptor-mediated endocytosis and to integrate into host cell genome and express viral genes stably and efficiently have made them attractive candidates for the transfer of foreign genes into mammalian cells (Ridgeway, 1988; Nicolas and Rubenstein, 1988; Baichwal and Sugden, 1986; Temin, 1986). The first viruses used as vectors were DNA viruses including the papovaviruses (simian virus 40, bovine papilloma virus, and polyoma) (Ridgeway, 1988; Baichwal and Sugden, 1986) and adenoviruses (Ridgeway, 1988; Baichwal and Sugden, 1986) and adeno-associated viruses. Retroviruses also are attractive gene transfer vehicles (Nicolas and Rubenstein, 1988; Temin, 1986) as are vaccina virus (Ridgeway, 1988) and adeno-associated virus (Ridgeway, 1988). Such vectors may be used to (i) transform cell lines in vitro for the purpose of expressing proteins of interest or (ii) to transform cells in vitro or in vivo to provide therapeutic polypeptides in a gene therapy scenario.

In a preferred embodiment, the vector is HSV. Because HSV is neurotropic, it has generated considerable interest in treating nervous system disorders. Moreover, the ability of HSV to establish latent infections in non-dividing neuronal cells without integrating in to the host cell chromosome or otherwise altering the host cell's metabolism, along with the existence of a promoter that is active during latency. And though much attention has focused on the neurotropic applications of HSV, this vector also can be exploited for other tissues.

Another factor that makes HSV an attractive vector is the size and organization of the genome. Because HSV is large, incorporation of multiple genes or expression cassettes is less problematic than in other smaller viral systems. In addition, the availability of different viral control sequences with varying performance (temporal, strength, etc.) makes it possible to control expression to a greater extent than in other systems. It also is an advantage that the virus has relatively few spliced messages, further easing genetic manipulations.

HSV also is relatively easy to manipulate and can be grown to high titers. Thus, delivery is less of a problem, both in terms of volumes needed to attain sufficient MOI and in a lessened need for repeat dosings. For a review of HSV as a gene therapy vector, see Glorioso et al., 1995.

IV. Methods for Screening

A. Inhibitors of ICP4 Anti-Apoptotic Activity

In one embodiment of the present invention, there are provided methods of screening compounds for activity against ICP4's anti-apoptotic activity. These screening methods will determine the cell pathology of target cells that express ICP4, both in the presence and absence of the test compound. At least three different assays may be employed, as discussed below.

First, one may look at DNA fragmentation using a separative method, e.g., chromatography or electrophoresis, to size fractionate the sample. As described in greater detail in the examples, an exemplary assay involves the isolation of DNA from cells, followed by agarose gel electrophoresis and staining with ethidium bromide. DNA fragmentation, characteristic of apoptosis, will be visualized as "ladders" containing a wide range of fragment sizes.

Second, one may employ terminal deoxynucleotidyl transferase mediated dUTP-biotin nick end labeling (TUNEL) assays to measures the integrity of DNA (Gorczyca, 1993). This assay measures the fragmentation of DNA by monitoring the incorporation of labeled UTP into broken DNA strands by the enzyme terminal transferase. The incorporation can be monitored by electroscopy or by cell sorting methodologies (e.g., FACS)

Third, one may examine cells using standard light or electron microscopy to assess the presence or absence of the cytopathologies characteristic of apoptosis. Those of skill in the art, applying standard methods of microscopy, will be able to assess cytopathology.

In each of these assays, a cell will be employed as the target for induction and inhibition of apoptosis. In one embodiment, the cell will be infected with HSV that expresses its own ICP4 protein. In a second embodiment, the cell will carry the α4 gene linked to a viral promoter. Infection with the appropriate virus will result in stimulation of the α4 gene and expression of ICP4. In these first two embodiments, the infection should induce apoptosis in the cell, and the expression of ICP4 should limit this effect. In a third embodiment, the cell will contain, as part of its own genetic material, an inducible version of the ICP4 gene (i.e., α4 linked to an inducible promoter). In this situation, it will be necessary to induce apoptosis via some other mechanism, such as hypothermia, and express ICP4 by inducing the promoter.

The cell is contacted with a candidate inhibitor substance in order to assess its effect on ICP4 activity. The substance may be contacted with the cell prior to, at the same time, or after the provision of ICP4. In some cases, the candidate inhibitor substance may be contacted with the cell directly. In other situations, depending on the nature and putative mechanism of action, the candidate inhibitor substance may be reformulated to provide improved uptake. For example, where antisense oligonucleotides are provided, these may advantageously be formulated in liposomes or as virally-encapsulated expression vehicles. Where polypeptides are to be tested, it may be advantageous to provide expression vectors encoding these molecules rather than the polypeptides themselves. Essentially, the most reasonable mechanism for delivering an effective amount of the candidate inhibitor substance to the proper intracellular site will be chosen. "Effective amount," for the purposes of the screening assay, is intended to mean an amount that will cause a detectable difference, and preferably a significant difference, in the cytopathology of the cell as compared to a similar treatment of the cell without the candidate inhibitor substance.

Once the candidate inhibitor substance has been provided to a cell that expresses ICP4, the evaluation of cytopathology may be undertaken. Depending on the type of assay used to examine cytopathology, it is possible to automate this process and test hundreds of candidates at the same time. For example, 96-well trays may be employed in which several wells are reserved for controls while the remainder comprise test substances, usually with each substance being tested at several different amounts.

V. Methods for the Inhibition of Apoptosis

In one embodiment of the present invention, there are provided methods for the inhibition of apoptosis in a cell. This is particularly useful where one seeks to immortalize a cell or, at a minimum, increase the longevity of a cell. This permits one to maintain that cell in culture for extended periods of time, perhaps indefinitely. Immortalized cells are useful primarily as factories for production of viral vectors or proteins of interest, but it also may be important to immortalize cell simply so that they may be studied in vitro with greater ease. In addition, though many viruses provide promise as gene therapeutic vectors, these vectors may trigger apoptosis in the cells they infect. Blocking virally-induced apoptosis will prevent cell death caused by these therapeutic vectors. As mentioned above, adenovirus, papilloma viruses, retrovirus, adeno-associated virus and HSV, for example, are candidate gene therapeutic vectors that could benefit from this application.

The general approach to inhibiting apoptosis, according to the present invention, will be to provide a cell with an ICP4 polypeptide, thereby permitting the inhibitory activity of ICP4 to take effect. While it is conceivable that the protein may be delivered directly, a preferred embodiment involves providing a nucleic acid encoding an ICP4 polypeptide, i.e., an α4 gene, to the cell. Following this provision, the ICP4 polypeptide is synthesized by the host cell's transcriptional and translational machinery, as well as any that may be provided by the expression construct. Cisacting regulatory elements necessary to support the expression of the α4 gene will be provided, as described above, in the form of an expression construct. It also is possible that, in the case of an HSV-infected cell, expression of the virally-encoded α4 could be stimulated or enhanced, or the expressed polypeptide stabilized, thereby achieving the same or similar effect.

In order to effect expression of constructs encoding α4 genes, the expression construct must be delivered into a cell. As described above in the discussion of viral vectors, one mechanism for delivery is via viral infection, where the expression construct is encapsidated in a viral particle which will deliver either a replicating or non-replicating nucleic acid. The preferred embodiment is an HSV vector, although virtually any vector would suffice. Similarly, where viral vectors are used to delivery other therapeutic genes, inclusion in these vectors of an α4 gene advantageously will protect the cell from virally induced apoptosis.

Several non-viral methods for the transfer of expression constructs into cultured mammalian cells also are contemplated by the present invention. These include calcium phosphate precipitation (Gopal, 1985), electroporation (Tur-Kaspa et al., 1986; Potter et al., 1984), direct microinjection (Harland and Weintraub, 1985), DNA-loaded liposomes (Nicolau and Sene, 1982; Fraley et al., 1979) and lipofectamine-DNA complexes, cell sonication (Fechheimer et al., 1987), gene bombardment using high velocity microprojectiles (Yang et. al., 1990), and receptor-mediated transfection (Wu and Wu, 1987; Wu and Wu, 1988). Some of these techniques may be successfully adapted for in vivo or ex vivo use, as discussed below.

In another embodiment of the invention, the expression construct may simply consist of naked recombinant DNA or plasmids. Transfer of the construct may be performed by any of the methods mentioned above which physically or chemically permeabilize the cell membrane. This is particularly applicable for transfer in vitro, but it may be applied to in vivo use as well. Another embodiment of the invention for transferring a naked DNA expression construct into cells may involve particle bombardment. This method depends on the ability to accelerate DNA coated microprojectiles to a high velocity allowing them to pierce cell membranes and enter cells without killing them (Klein et al., 1987). Several devices for accelerating small particles have been developed. One such device relies on a high voltage discharge to generate an electrical current, which in turn provides the motive force (Yang et al., 1990). The microprojectiles used have consisted of biologically inert substances such as tungsten or gold beads.

In a further embodiment of the invention, the expression construct may be entrapped in a liposome. Liposomes are vesicular structures characterized by a phospholipid bilayer membrane and an inner aqueous medium. Multilamellar liposomes have multiple lipid layers separated by aqueous medium. They form spontaneously when phospholipids are suspended in an excess of aqueous solution. The lipid components undergo self-rearrangement before the formation of closed structures and entrap water and dissolved solutes between the lipid bilayers (Ghosh and Bachhawat, 1991). Also contemplated are lipofectamine-DNA complexes.

Liposome-mediated nucleic acid delivery and expression of foreign DNA in vitro has been very successful. Wong et al. (1980) demonstrated the feasibility of liposome-mediated delivery and expression of foreign DNA in cultured chick embryo, HeLa and hepatoma cells. In certain embodiments of the invention, the liposome may be complexed with a hemagglutinating virus (HVJ). This has been shown to facilitate fusion with the cell membrane and promote cell entry of liposome-encapsulated DNA (Kaneda et al., 1989). In other embodiments, the liposome may be complexed or employed in conjunction with nuclear non-histone chromosomal proteins (HMG-1) (Kato et al., 1991). In yet further embodiments, the liposome may be complexed or employed in conjunction with both HVJ and HMG-1. In other embodiments, the delivery vehicle may comprise a ligand and a liposome. Where a bacterial promoter is employed in the DNA construct, it also will be desirable to include within the liposome an appropriate bacterial polymerase.

Other expression constructs which can be employed to deliver a nucleic acid encoding an α4 transgene into cells are receptor-mediated delivery vehicles. These take advantage of the selective uptake of macromolecules by receptor-mediated endocytosis in almost all eukaryotic cells. Because of the cell type-specific distribution of various receptors, the delivery can be highly specific (Wu and Wu, 1993).

Receptor-mediated gene targeting vehicles generally consist of two components: a cell receptor-specific ligand and a DNA-binding agent. Several ligands have been used for receptor-mediated gene transfer. The most extensively characterized ligands are asialoorosomucoid (ASOR) (Wu and Wu, 1987) and transferrin (Wagner et al., 1990). Recently, a synthetic neoglycoprotein, which recognizes the same receptor as ASOR, has been used as a gene delivery vehicle (Ferkol et al., 1993; Perales et al., 1994). Mannose can be used to target the mannose receptor on liver cells. Also, antibodies to CD5 (CLL), CD22 (lymphoma), CD25 (T-cell leukemia) and MAA (melanoma) can similarly be used as targeting moieties. In other embodiments, the delivery vehicle may comprise a ligand and a liposome.

Primary mammalian cell cultures may be prepared in various ways. In order for the cells to be kept viable while in vitro and in contact with the expression construct, it is necessary to ensure that the cells maintain contact with the correct ratio of oxygen and carbon dioxide and nutrients but are protected from microbial contamination. Cell culture techniques are well documented and are disclosed herein by reference (Freshner, 1992).

One embodiment of the foregoing involves the use of gene transfer to immortalize cells for the production of proteins. The gene for the protein of interest may be transferred as described above into appropriate host cells followed by culture of cells under the appropriate conditions. The gene for virtually any polypeptide may be employed in this manner. The generation of recombinant expression vectors, and the elements included therein, are discussed above. Alternatively, the protein to be produced may be an endogenous protein normally synthesized by the cell in question.

Examples of useful mammalian host cell lines are Vero and HeLa cells and cell lines of Chinese hamster ovary, W138, BHK, COS-7, 293, HepG2, 3T3, RIN and MDCK cells. In addition, a host cell strain may be chosen that modulates the expression of the inserted sequences, or modifies and process the gene product in the manner desired. Such modifications (e.g., glycosylation) and processing (e.g., cleavage) of protein products may be important for the function of the protein. Different host cells have characteristic and specific mechanisms for the post-translational processing and modification of proteins. Appropriate cell lines or host systems can be chosen to insure the correct modification and processing of the foreign protein expressed.

A number of selection systems may be used including, but not limited to, HSV thymidine kinase, hypoxanthine-guanine phosphoribosyltransferase and adenine phosphoribosyltransferase genes, in tk-, hgprt- or aprt- cells, respectively. Also, anti-metabolite resistance can be used as the basis of selection for dhfr, that confers resistance to; gpt, that confers resistance to mycophenolic acid; neo, that confers resistance to the aminoglycoside G418; and hygro, that confers resistance to hygromycin.

Animal cells can be propagated in vitro in two modes: as non-anchorage dependent cells growing in suspension throughout the bulk of the culture or as anchorage-dependent cells requiring attachment to a solid substrate for their propagation (i.e., a monolayer type of cell growth).

Non-anchorage dependent or suspension cultures from continuous established cell lines are the most widely used means of large scale production of cells and cell products. However, suspension cultured cells have limitations, such as tumorigenic potential and lower protein production than adherent cells.

Large scale suspension culture of mammalian cells in stirred tanks is a common method for production of recombinant proteins. Two suspension culture reactor designs are in wide use--the stirred reactor and the airlift reactor. The stirred design has successfully been used on an 8000 liter capacity for the production of interferon (Phillips et al., 1985; Mizrahi, 1983). Cells are grown in a stainless steel tank with a height-to-diameter ratio of 1:1 to 3:1. The culture is usually mixed with one or more agitators, based on bladed disks or marine propeller patterns. Agitator systems offering less shear forces than blades have been described. Agitation may be driven either directly or indirectly by magnetically coupled drives. Indirect drives reduce the risk of microbial contamination through seals on stirrer shafts.

The airlift reactor, also initially described for microbial fermentation and later adapted for mammalian culture, relies on a gas stream to both mix and oxygenate the culture. The gas stream enters a riser section of the reactor and drives circulation. Gas disengages at the culture surface, causing denser liquid free of gas bubbles to travel downward in the downcomer section of the reactor. The main advantage of this design is the simplicity and lack of need for mechanical mixing. Typically, the height-to-diameter ratio is 10:1. The airlift reactor scales up relatively easily, has good mass transfer of gases and generates relatively low shear forces.

VI. Methods for the Induction of Apoptosis

In another embodiment of the present invention, there is contemplated the method of inducing apoptosis in HSV-infected cells, i.e., blocking the function of ICP4. In this way, it may be possible to curtail viral infection by bringing about a premature death of the infected cell. In addition, it may prove effective to use this sort of therapeutic intervention in combination with more traditional chemotherapies, such as the administration acyclovir.

The general form that this aspect of the invention will take is the provision, to a cell, of an agent that will inhibit ICP4 function. Four such agents are contemplated. First, one may employ an antisense nucleic acid that will hybridize either to the α4 gene or the α4 transcript, thereby preventing transcription or translation, respectively. The considerations relevant to the design of antisense constructs have been presented above. Second, one may utilize an ICP4-binding protein or peptide, for example, a peptidomimetic or an antibody that binds immunologically to an ICP4, the binding of either will block or reduce the activity of an ICP4. The methods of making and selecting peptide binding partners and antibodies are well known to those of skill in the art. Third, one may provide to the cell an antagonist of ICP4, for example, the transactivation target sequence, alone or coupled to another agent. And fourth, one may provide an agent that binds to the ICP4 target without the same functional result as would arise with ICP4 binding.

Provision of an α4 gene, an ICP4-binding protein, or an ICP4 antagonist, would be according to any appropriate pharmaceutical route. The formulation of such compositions and their delivery to tissues is discussed below. The method by which the nucleic acid, protein or chemical is transferred, along with the preferred delivery route, will be selected based on the particular site to be treated. Those of skill in the art are capable of determining the most appropriate methods based on the relevant clinical considerations.

Many of the gene transfer techniques that generally are applied in vitro can be adapted for ex vivo or in vivo use. For example, selected organs including the liver, skin, and muscle tissue of rats and mice have been bombarded in vivo (Yang et al., 1990; Zelenin et al., 1991). Naked DNA also has been used in clinical settings to effect gene therapy. These approaches may require surgical exposure of the tumor tissue or direct intratumoral injection. Nicolau et al. (1987) accomplished successful liposome-mediated gene transfer in rats after intravenous injection.

Dubensky et al. (1984) successfully injected polyomavirus DNA in the form of CaPO₄ precipitates into liver and spleen of adult and newborn mice demonstrating active viral replication and acute infection. Benvenisty and Neshif (1986) also demonstrated that direct intraperitoneal injection of CaPO₄ precipitated plasmids results in expression of the transfected genes. Thus, it is envisioned that DNA encoding an antisense construct also may be transferred in a similar manner in vivo.

Where the embodiment involves the use of an antibody that recognizes an ICP4 polypeptide, consideration must be given to the mechanism by which the antibody is introduced into the cell cytoplasm. This can be accomplished, for example, by providing an expression construct that encodes a single-chain antibody version of the antibody to be provided. Most of the discussion above relating to expression constructs for antisense versions of α4 genes will be relevant to this aspect of the invention. Alternatively, it is possible to present a bifunctional antibody, where one antigen binding arm of the antibody recognizes an ICP4 polypeptide and the other antigen binding arm recognizes a receptor on the surface of the cell to be targeted. Examples of suitable receptors would be an HSV glycoprotein such as gB, gC, gD, or gH. In addition, it may be possible to exploit the Fc-binding function associated with HSV gE, thereby obviating the need to sacrifice one arm of the antibody for purposes of cell targeting.

Advantageously, one may combine this approach with more conventional chemotherapeutic options. Acyclovir is an active agent against HSV-1 and HSV-2. The drug inhibits actively replicating herpes virus but is not active against latent virus. Acyclovir is available in three formulations. For topical use, a five percent ointment produces therapeutic drug levels in mucocutaneous lesions. For systemic use, acyclovir may be administered orally or intravenously. The usual intravenous dosage in adults with normal renal function is 5 mg/kg infuised at a constant rate over one hour and given every eight hours; this dosage produces peak plasma levels at about 10 g/ml. For HSV encephalitis, twice this dose is used. The usual adult oral dosage is 200 mg, five times daily, which produces plasma levels that are less than 10% as high as those achieved with intravenous administration; even these levels are inhibitory to the virus, however. Acyclovir is given in an oral dosage of 800 mg five times daily for the treatment of herpes zoster, although oral administration generally is reserved for patients with severe symptoms. A three percent opthalmic preparation produces inhibitory drug levels in the aqueous humor and is effective for herpes keratitis.

VII. Methods for the Inhibition of Virus-Induced Cell Death In Vivo

In another embodiment of the present invention, there are provided methods for the inhibition of cell death induced in vivo by any cause comprising the provision of ICP4 polypeptides or α4 genes. Also contemplated in this aspect of the invention is the stimulation of viral ICP4 expression, or stabilization of the virally-expressed ICP4 polypeptide. Though inhibition of apoptosis generally is thought of as advantageous to the virus, it may be desirable to effect this result as part of a method of treating a viral infection. For example, if the host cell remains viable, the virus may continue to replicate; alternatively, if apoptosis were occurring, the virus might be inclined to "go latent" in the neural ganglia, where chemotherapeutic intervention is not helpful. Thus, by preventing early death of the cell, ICP4 may cause the virus to remain susceptible to treatment where it otherwise would escape.

The mechanisms for delivering ICP4 proteins and nucleic acids to a cell are discussed elsewhere in this document and need not be repeated here. The use of standard chemotherapeutics has been presented in the preceding section, and is incorporated in this section.

VIII. Pharmaceuticals and In vivo Methods for the Treatment of Disease

Aqueous pharmaceutical compositions of the present invention will have an effective amount of an α4 expression construct, an antisense α4 expression construct, an expression construct that encodes a therapeutic gene along with α4, a protein that inhibits ICP4 function, such as an anti-ICP4 antibody, or an ICP4 polypeptide. Such compositions generally will be dissolved or dispersed in a pharmaceutically acceptable carrier or aqueous medium. An "effective amount," for the purposes of therapy, is defined at that amount that causes a clinically measurable difference in the condition of the subject. This amount will vary depending on the substance, the condition of the patient, the type of treatment, the location of the lesion, etc.

The phrases "pharmaceutically or pharmacologically acceptable" refer to molecular entities and compositions that do not produce an adverse, allergic or other untoward reaction when administered to an animal, or human, as appropriate. As used herein, "pharmaceutically acceptable carrier" includes any and all solvents, dispersion media, coatings, antibacterial and antiftugal agents, isotonic and absorption delaying agents and the like. The use of such media and agents for pharmaceutical active substances is well known in the art. Except insofar as any conventional media or agent is incompatible with the active ingredients, its use in the therapeutic compositions is contemplated. Supplementary active ingredients, such as other anti-cancer agents, can also be incorporated into the compositions.

In addition to the compounds formulated for parenteral administration, such as those for intravenous or intramuscular injection, other pharmaceutically acceptable forms include, e.g., tablets or other solids for oral administration; time release capsules; and any other form currently used, including cremes, lotions, mouthwashes, inhalants and the like.

The active compounds of the present invention will often be formulated for parenteral administration, e.g., formulated for injection via the intravenous, intramuscular, subcutaneous, or even intraperitoneal routes. The preparation of an aqueous composition that contains glycosylceramide synthesis inhibitory compounds alone or in combination with a chemotherapeutic agent as active ingredients will be known to those of skill in the art in light of the present disclosure. Typically, such compositions can be prepared as injectables, either as liquid solutions or suspensions; solid forms suitable for using to prepare solutions or suspensions upon the addition of a liquid prior to injection can also be prepared; and the preparations can also be emulsified.

Solutions of the active compounds as free base or pharmacologically acceptable salts can be prepared in water suitably mixed with a surfactant, such as hydroxypropylcellulose. Dispersions can also be prepared in glycerol, liquid polyethylene glycols, and mixtures thereof and in oils. Under ordinary conditions of storage and use, these preparations contain a preservative to prevent the growth of microorganisms.

The pharmaceutical forms suitable for injectable use include sterile aqueous solutions or dispersions; formulations including sesame oil, peanut oil or aqueous propylene glycol; and sterile powders for the extemporaneous preparation of sterile injectable solutions or dispersions. In many cases, the form must be sterile and must be fluid to the extent that easy syringability exists. It must be stable under the conditions of manufacture and storage and must be preserved against the contaminating action of microorganisms, such as bacteria and fungi.

The active compounds may be formulated into a composition in a neutral or salt form. Pharmaceutically acceptable salts, include the acid addition salts (formed with the free amino groups of the protein) and which are formed with inorganic acids such as, for example, hydrochloric or phosphoric acids, or such organic acids as acetic, oxalic, tartaric, mandelic, and the like. Salts formed with the free carboxyl groups can also be derived from inorganic bases such as, for example, sodium, potassium, ammonium, calcium, or ferric hydroxides, and such organic bases as isopropylamine, trimethylamine, histidine, procaine and the like.

The carrier also can be a solvent or dispersion medium containing, for example, water, ethanol, polyol (for example, glycerol, propylene glycol, and liquid polyethylene glycol, and the like), suitable mixtures thereof, and vegetable oils. The proper fluidity can be maintained, for example, by the use of a coating, such as lecithin, by the maintenance of the required particle size in the case of dispersion and by the use of surfactants. The prevention of the action of microorganisms can be brought about by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenol, sorbic acid, thimerosal, and the like. In many cases, it will be preferable to include isotonic agents, for example, sugars or sodium chloride. Prolonged absorption of the injectable compositions can be brought about by the use in the compositions of agents delaying absorption, for example, aluminum monostearate and gelatin.

Sterile injectable solutions are prepared by incorporating the active compounds in the required amount in the appropriate solvent with various of the other ingredients enumerated above, as required, followed by filtered sterilization. Generally, dispersions are prepared by incorporating the various sterilized active ingredients into a sterile vehicle which contains the basic dispersion medium and the required other ingredients from those enumerated above. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum-drying and freeze-drying techniques which yield a powder of the active ingredient plus any additional desired ingredient from a previously sterile-filtered solution thereof.

In certain cases, the therapeutic formulations of the invention could also be prepared in forms suitable for topical administration, such as in cremes and lotions. These forms may be used for treating skin-associated diseases, such as various sarcomas. In certain other cases, the formulation will be geared for administration to the central nervous system, e.g., the brain.

Upon formulation, solutions will be administered in a manner compatible with the dosage formulation and in such amount as is therapeutically effective. The formulations are easily administered in a variety of dosage forms, such as the type of injectable solutions described above, with even drug release capsules and the like being employable.

For parenteral administration in an aqueous solution, for example, the solution should be suitably buffered if necessary and the liquid diluent first rendered isotonic with sufficient saline or glucose. These particular aqueous solutions are especially suitable for intravenous, intramuscular, subcutaneous and intraperitoneal administration. In this connection, sterile aqueous media which can be employed will be known to those of skill in the art in light of the present disclosure. For example, one dosage could be dissolved in 1 mL of isotonic NaCl solution and either added to 1000 mL of hypodermoclysis fluid or injected at the proposed site of infusion, (see for example, "Remington's Pharmaceutical Sciences" 15th Edition, pages 1035-1038 and 1570-1580). Some variation in dosage will necessarily occur depending on the condition of the subject being treated. The person responsible for administration will, in any event, determine the appropriate dose for the individual subject.

IX. Examples

The following examples are included to demonstrate preferred embodiments of the present invention. It should be appreciated by those of skill in the art that that techniques disclosed in the examples which follow represent techniques discovered by the inventors to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar results without departing from the spirit and scope of the invention.

EXAMPLE 1 MATERIALS AND METHODS

Cells. Vero cells were originally obtained from J. McCleland. HSV-1(F) is the prototype HSV-1 strain used in this study (Ejercito et al., 1968). E5, obtained from N. DeLuca of the University of Pittsburgh, is a Vero cell line expressing ICP4 under its own promoter (DeLuca et al., 1985). Expression of ICP4 is transactivated by the infecting virus.

Viruses. HSV-1(F), the prototype HSV-1 strain used in this study, like most wild-type isolates with a history of limited cell culture passages, carries a temperature-sensitive mutation in ICP4 (Ejercito et al., 1968). At the nonpernissive temperature (39.5° C.) it is defective in the expression of β and γ genes. The HSV-1 mutant d120 (obtained from N. DeLuca) carries a deletion in both copies of the ICP4 gene, and can grow only in cell lines that express ICP4 (DeLuca et al., 1985). The HSV-1 tsHAl carries a temperature-sensitive mutation in ICP8, a protein essential for viral DNA replication (Conley et al., 1981). At the nonpermissive temperature (39.5° C.) it is defective in DNA synthesis and does not express γ₂ genes dependent on viral DNA synthesis for their expression. A schematic representation of the genome of HSV-1 is shown in FIG. 1.

Electron photomicroscopy. Vero cells infected with HSV-1(F) or d120 were incubated for 20 hrs at 37° C. Cells were fixed in 2% glutaraldehyde in PBS for 60 min at 4° C., post-fixed with 1% osmium tetroxide, en bloc stained with uranyl acetate (5 mg/ml), dehydrated in acetone, and embedded in Epon 812. Thin sections were examined either unstained or poststained with uranyl acetate and lead hydroxide. The cells were photographed at 6000× in a Siemens 101 electron microscope.

Light photomicroscopy. Cells were labeled with biotinylated dUTP. At indicated times the cells were fixed in ice-cold methanol at -20° C. and air-dried, then rinsed in phosphate buffered saline, reacted for 15 min at room temperature with 40 ml of a solution containing 1× terminal transferase buffer (Promega), 1 mM CoCl₂, 0.05 mg/ml bovine serum albumin (BSA), 0.5 nmoles biotin-16-dUTP (Boehringer Mannheim Biochemicals) and 3 units of terminal transferase (TdT, Promega), rinsed extensively in PBS, reacted for 30 min at room temperature with 40 ml of a solution containing Texas red-conjugated avidin in 4× SSC (1× SSC is 0.15M NaCl, 0.015M Na-citrate), 0.1% Triton X-100, 5% (w/v) nonfat dry milk, extensively rinsed with PBS, mounted in 10% PBS in glycerol and examined under a Zeiss confocal fluorescence microscope. The images were captured under identical settings with the software provided by Zeiss and printed in a Tektronix 440 phaser printer. Cells were mock infected, 37° C., 20 hrs; infected with d120 virus, 37° C. 20 hrs; infected with HSV-1(F), 37° C., 20 hrs; infected with d120 virus, 37° C. 30 hrs; mock-infected, 39.5° C., 30 hrs.; infected with d120 virus, 39.5° C., 30 hrs.; and infected with HSV-1(F), 39.5° C., 30 hrs.

DNA Fragmentation Assay. Vero cells or E5 cells were infected with HSV-1(F), d120 mutant, or HSV-1 tsHA1 mutant and maintained at 37° C. or 39.5° C. in the absence or in the presence of phosphonoacetic acid. At 30 hrs after infection, 2×10⁶ cells per sample were collected, washed in PBS, lysed in a solution containing 10 mM Tris-HCl, pH 8.0, 10 mM EDTA, and 0.5% Triton X-100, and centrifuged at 12,000 rpm for 25 min in an Eppendorf microcentrifuge to pellet chromosomal DNA. Supernatant fluids were digested with 0.1 mg RNase A per ml at 37° C. for 1 hr, for 2 hrs with 1 mg proteinase K per ml at 50° C. in the presence of 1% sodium dodecylsulphate (SDS), extracted with phenol and chloroform, and precipitated in cold ethanol and subjected to electrophoresis on horizontal 1.5% agarose gels containing 5 mg of ethidium bromide per ml. DNA was visualized by UV light transillumination. Photographs were taken with the aid of a computer-assisted image processor (Eagle Eye II, Stratagene).

EXAMPLE 2 RESULTS

An HSV-1 mutant deleted in ICP4 induces apoptosis. In the first series of studies, Vero cells infected with wild-type or the d120 mutant were examined for morphologic evidence of apoptosis. Vero cells were fixed and harvested at 20 to 24 hrs after infection with wild-type or d120, embedded, sectioned, and examined in a Siemens 101 electron microscope. The cells infected with wild-type virus showed typical infected cell morphology, i.e., marginated chromatin, separation of inner and outer nuclear membranes, and accumulation of virus particles in some but not all cells. Cells infected with the d120 deletion mutant exhibited extensive condensation of chromatin, obliteration of the nuclear membrane, and extensive vacuolization and blebbing of the cytoplasm. It was estimated that approximately 40 to 50% of the infected cells exhibited some or all of the morphologic changes described above.

In the second series of studies, Vero cells were mock-infected or infected with 10 PFU of either the wild-type or the d120 mutant virus per cell. After 20 hrs of incubation at 37° C. the cells were fixed, labeled with biotinylated dUTP in the presence of terminal transferase, and then reacted with fluorescent avidin. Mock-infected cells or cells infected with wild-type virus showed no sign of labeling with biotinylated dUTP by terminal transferase, whereas cells infected with d120 and maintained at the same temperature showed extensive fluorescence due to the reaction of fluorescent avidin to biotinylated dUTP incorporated at the DNA termini created by the cleavage of DNA.

In the third series of studies, replicate Vero cell cultures were infected with 10 PFU of either HSV-1(F) or d120 per cell and incubated at 37° C. The study also included a Vero cell culture infected with HSV-1(F), overlaid with medium containing 300 μg of phosphonoacetate per ml and incubated at 37° C., and a set of Vero cell cultures infected with 10 PFU of HSV-1 tsHA1 and incubated at either 37° C. or 39.5° C. This concentration of phosphonoacetate completely inhibits viral DNA synthesis and blocks the expression of γ₂ genes dependent on viral synthesis for their expression. The cells were harvested at 30 hrs after infection, lysed, and centrifuged to pellet the chromosomal DNA. The supernatant fluids were processed as described above and subjected to electrophoresis in agarose gels to test for the presence of soluble, fragmented DNA.

The results were as follows. Cells infected with d120 deletion mutant yielded high amounts of fragmented DNA which were readily visible on agarose gels stained with ethidium bromide. These ladders were not seen in agarose gels containing electrophoretically separated extracts of wild-type infected cells or E5 cells infected with d120. When Vero cells were incubated in medium containing phosphonoacetate, fragmented DNA was detected from cells infected with d120 mutant but not with the wild-type. Fragmented DNA was visible in extracts of mock-infected cells incubated at 39.5° C., but not in cells infected with HSV-1tsHA1 and incubated at the same temperature.

From this series of studies, it is concluded that (i) HSV-1 is capable of inducing the morphologic and biochemical changes characteristic of apoptosis and these changes are prominent in cells infected with a mutant lacking ICP4; (ii) wild-type virus does not induce apoptosis indicating that ICP4 or a protein expressed subsequently is able to protect cells from apoptosis; (iii) the protective, anti-apoptotic effect is a viral function which does not depend on the onset of viral DNA synthesis; (iv) DNA degradation typical of apoptosis was observed upon incubation at 39.5° C. in mock-infected but not HSV-1tsHA1 infected cells, which suggests that prolonged incubation at the elevated temperature can induce apoptosis that is blocked by a viral function expressed early.

ICP4 expresses an anti-apoptotic function. In a fourth series of studies, Vero or E5 cells were mock infected or infected with 10 PFU per cell with either HSV-1(F) or d120. The cells were incubated at 39.5° C. for 30 hrs. The rationale of these studies was as follows. As noted in Example 1, HSV-1(F) carries a ts lesion in the α4 gene and at the nonpermissive temperature (39.5° C.) expresses only α genes. The α4 gene resident in the E5 cell line and the d120 mutant virus lacking the α4 gene were derived from the HSV-1 (KOS) strain which does not exhibit the ts phenotype. In addition, the α4 gene resident in the E5 cell line is induced after infection and is not expressed in uninfected cells. In the first series of studies, the cells were harvested, lysed, centrifuged to sediment chromosomal DNA and the supernatant fluids were processed as described in Example 1 and subjected to electrophoresis in agarose gels.

The results were as follows. Fragmented DNA was present in lanes containing electrophoretically separated extracts of mock-infected Vero cells, Vero cells infected with d120 mutant, and the mock infected E5 cells. Fragmented DNA was not detected in Vero cells infected with wild-type virus, or in E5 cells infected with either d120 mutant virus or HSV-1(F) virus.

In the second series of studies Vero cells were mock infected, or infected with either d120 or with wild-type virus. After 30 hrs of incubation at 39.5° C., the cells were fixed and labeled with biotinylated dUTP by terminal transferase, and reacted with fluorescent avidin. Fluorescence was detected in mock-infected or infected with d120 mutant, but not in cells infected with wild-type virus.

These studies allowed permit the conclusion conclude that HSV-1(F) α4 gene encodes a function which blocks apoptosis reflected in the degradation of DNA, and that this function is separable from the repressor and transactivator functions of ICP4 which are affected by the temperature sensitive lesion of the α4 gene of HSV-1 (F).

A summary of the results is provided in Table 4. Induction of (+), or protection from (-) apoptosis is indicated upon conditions (infecting virus and incubation temperature) which induce apoptosis in Vero and E5 cell lines. "nt" indicates not tested.

                  TABLE 4     ______________________________________             VERO   VERO             (37° C.)                    (39° C.)                            E5 (37° C.)                                       E5 (39.5° C.)     ______________________________________     MOCK      -        +       -        +     HSV-1(F)  -        -       -        -     HSV-1 d120               +        +       -        -     HSV-1 tsHA1               -        -       nt       nt     ______________________________________

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    __________________________________________________________________________     SEQUENCE LISTING     (1) GENERAL INFORMATION:     (iii) NUMBER OF SEQUENCES: 2     (2) INFORMATION FOR SEQ ID NO:1:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 4257 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:     GCTGCTCCTCCTTCCCGCCGGCCCCTGGGACTATATGAGCCCGAGGACGCCCCGATCGTC60     CACACGGAGCGCGGCTGCCGACACGGATCCACGACCCGACGCGGGACCGCCAGAGACAGA120     CCGTCAGACGCTCGCCGCGCCGGGACGCCGATACGCGGACGAAGCGCGGGAGGGGGATCG180     GCCGTCCCTGTCCTTTTTCCCACCCAAGCATCGACCGGTCCGCGCTAGTTCCGCGTCGAC240     GGCGGGGGTCGTCGGGGTCCGTGGGTCTCGCCCCCTCCCCCCATCGAGAGTCCGTAGGTG300     ACCTACCGTGCTACGTCCGCCGTCGCAGCCGTATCCCCGGAGGATCGCCCCGCATCGGCG360     ATGGCGTCGGAGAACAAGCAGCGCCCCGGCTCCCCGGGCCCCACCGACGGGCCGCCGCCC420     ACCCCGAGCCCAGACCGCGACGAGCGGGGGGCCCTCGGGTGGGGCGCGGAGACGGAGGAG480     GGCGGGGACGACCCCGACCACGACCCCGACCACCCCCACGACCTCGACGACGCCCGGCGG540     GACGGGAGGGCCCCCGCGGCGGGCACCGACGCCGGCGAGGACGCCGGGGACGCCGTCTCG600     CCGCGACAGCTGGCTCTGCTGGCCTCCATGGTAGAGGAGGCCGTCCGGACGATCCCGACG660     CCCGACCCCGCGGCCTCGCCGCCCCGGACCCCCGCCTTTCGAGCCGACGACGATGACGGG720     GACGAGTACGACGACGCAGCCGACGCCGCCGGCGACCGGGCCCCGGCCCGGGGCCGCGAA780     CGGGAGGCCCCGCTACGCGGCGCGTATCCGGACCCCACGGACCGCCTGTCGCCGCGCCCG840     CCGGCCCAGCCGCCGCGGAGACGTCGTCACGGCCGGTGGCGGCCATCGGCGTCATCGACC900     TCGTCGGACTCCGGGTCCTCGTCCTCGTCGTCCGCATCCTCTTCGTCCTCGTCGTCCGAC960     GAGGACGAGGACGACGACGGCAACGACGCGGCCGACCACGCACGCGAGGCGCGGGCCGTC1020     GGGCGGGGTCCGTCGAGCGCGGCGCCGGCAGCCCCCGGGCGGACGCCGCCCCCGCCCGGG1080     CCACCCCCCCTCTCCGAGGCCGCGCCCAAGCCCCGGGCGGCGGCGAGGACCCCCGCGGCC1140     TCCGCGGGCCGCATCGAGCGCCGCCGGGCCCGCGCGGCGGTGGCCGGCCGCGACGCCACG1200     GGCCGCTTCACGGCCGGGCAGCCCCGGCGGGTCGAGCTGGACGCCGACGCGACCTCCGGC1260     GCCTTCTACGCGCGCTATCGCGACGGGTACGTCAGCGGGGAGCCGTGGCCCGGCGCCGGG1320     CCCCCGCCCCCGGGGCGGGTGCTGTACGGCGGCCTGGGCGACAGCCGCCCGGGCCTCTGG1380     GGGGCGCCCGAGGCGGAGGAGGCGCGACGCCGGTTCGAGGCCTCGGGCGCCCCGGCGGCC1440     GTGTGGGCGCCCGAGCTGGGCGACGCCGCGCAGCAGTACGCCCTGATCACGCGGCTGCTG1500     TACACCCCGGACGCGGAGGCCATGGGGTGGCTCCAGAACCCGCGCGTGGTCCCCGGGGAC1560     GTGGCGCTGGACCAGGCCTGCTTCCGGATCTCGGGCGCCGCGCGCAACAGCAGCTCCTTC1620     ATCACCGGCAGCGTGGCGCGGGCCGTGCCCCACCTGGGCTACGCCATGGCGGCCGGCCGC1680     TTCGGCTGGGGCCTGGCGCACGCGGCGGCCGCCGTGGCCATGAGCCGCCGATACGACCGC1740     GCGCAGAAGGGCTTCCTGCTGACCAGCCTGCGCCGCGCCTACGCGCCCCTGTTGGCGCGC1800     GAGAACGCGGCGCTGACGGGGGCCGCGGGGAGCCCCGGCGCCGGCGCAGATGACGAGGGG1860     GTCGCCGCCGTCGCCGCCGCCGCACCGGGCGAGCGCGCGGTGCCCGCCGGGTACGGCGCC1920     GCGGGGATCCTCGCCGCCCTGGGGCGGCTGTCCGCCGCGCCCGCCTCCCCCGCGGGGGGC1980     GACGACCCCGACGCCGCCCGCCACGCCGACGCCGACGACGACGCCGGGCGCCGCGCCCAG2040     GCCGGCCGCGTGGCCGTCGAGTGCCTGGCCGCCTGCCGCGGGATCCTGGAGGCGCTGGCC2100     GAGGGCTTCGACGGCGACCTGGCGGCCGTCCCGGGGCTGGCCGGGGCCCGGCCCGCCAGC2160     CCCCCGCGGCCGGAGGGACCCGCGGGCCCCGCTTCCCCGCCGCCGCCGCACGCCGACGCG2220     CCCCGCCTGCGCGCGTGGCTGCGCGAGCTGCGGTTCGTGCGCGACGCGCTGGTGCTCATG2280     CGCCTGCGCGGGGACCTGCGCGTGGCCGGCGGCAGCGAGGCCGCCGTGGCCGCCGTGCGC2340     GCCGTGAGCCTGGTCGCCGGGGCCCTGGGCCCCGCGCTGCCGCGGGACCCGCGCCTGCCG2400     AGCTCCGCGGCCGCCGCCGCCGCGGACCTGCTGTTTGACAACCAGAGCCTGCGCCCCCTG2460     CTGGCGGCGGCGGCCAGCGCACCGGACGCCGCCGACGCGCTGGCGGCCGCCGCCGCCTCC2520     GCCGCGCCGCGGGAGGGGCGCAAGCGCAAGAGTCCCGGCCCGGCCCGGCCGCCCGGAGGC2580     GGCGGCCCGCGACCCCCGAAGACGAAGAAGAGCGGCGCGGACGCCCCCGGCTCGGACGCC2640     CGCGCCCCCCTCCCCGCGCCCGCGCCCCCCTCCACGCCCCCGGGGCCCGAGCCCGCCCCC2700     GCCCAGCCCGCGGCGCCCCGGGCCGCCGCGGCGCAGGCCCGCCCGCGCCCCGTGGCCGTG2760     TCGCGCCGGCCCGCCGAGGGCCCCGACCCCCTGGGCGGCTGGCGGCGGCAGCCCCCGGGG2820     CCCAGCCACACGGCGGCGCCCGCGGCCGCCGCCCTGGAGGCCTACTGCTCCCCGCGCGCC2880     GTGGCCGAGCTCACGGACCACCCGCTGTTCCCCGTCCCCTGGCGACCGGCCCTCATGTTT2940     GACCCGCGGGCCCTGGCCTCGATCGCCGCGCGGTGCGCCGGGCCCGCCCCCGCCGCCCAG3000     GCCGCGTGCGGCGGCGGCGACGACGACGATAACCCCCACCCCCACGGGGCCGCCGGGGGC3060     CGCCTCTTTGGCCCCCTGCGCGCCTCGGGCCCGCTGCGCCGCATGGCGGCCTGGATGCGC3120     CAGATCCCCGACCCCGAGGACGTGCGCGTGGTGGTGCTGTACTCGCCGCTGCCGGGCGAG3180     GACCTGGCCGGCGGCGGGGCCTCGGGGGGGCCGCCGGAGTGGTCCGCCGAGCGCGGCGGG3240     CTGTCCTGCCTGCTGGCGGCCCTGGCCAACCGGCTGTGCGGGCCGGACACGGCCGCCTGG3300     GCGGGCAATTGGACCGGCGCCCCCGACGTGTCGGCGCTGGGCGCACAGGGCGTGCTGCTG3360     CTGTCCACGCGGGACCTGGCCTTCGCCGGGGCCGTGGAGTTTCTGGGGCTGCTCGCCAGC3420     GCCGGCGACCGGCGGCTCATCGTGGTCAACACCGTGCGCGCCTGCGACTGGCCCGCCGAC3480     GGGCCCGCGGTGTCGCGGCAGCACGCCTACCTGGCGTGCGAGCTGCTGCCCGCCGTGCAG3540     TGCGCCGTGCGCTGGCCGGCGGCGCGGGACCTGCGCCGCACGGTGCTGGCCTCGGGCCGC3600     GTGTTCGGCCCGGGGGTCTTCGCGCGCGTGGAGGCCGCGCACGCGCGCCTGTACCCCGAC3660     GCGCCGCCGCTGCGCCTGTGCCGCGGCGGCAACGTGCGCTACCGCGTGCGCACGCGCTTC3720     GGCCCGGACACGCCGGTGCCCATGTCCCCGCGCGAGTACCGCCGGGCCGTGCTGCCGGCG3780     CTGGACGGCCGGGCGGCGGCCTCGGGGACCACCGACGCCATGGCGCCCGGCGCGCCGGAC3840     TTCTGCGAGGAGGAGGCCCACTCGCACGCCGCCTGCGCGCGCTGGGGCCTGGGCGCGCCG3900     CTGCGGCCCGTGTACGTGGCGCTGGGGCGCGAGGCGGTGCGCGCCGGCCCGGCCCGGTGG3960     CGCGGGCCGCGGAGGGACTTTTGCGCCCGCGCCCTGCTGGAGCCCGACGACGACGCCCCC4020     CCGCTGGTGCTGCGCGGCGACGACGACGGCCCGGGGGCCCTGCCGCCGGCGCCGCCCGGG4080     ATTCGCTGGGCCTCGGCCACGGGCCGCAGCGGCACCGTGCTGGCGGCGGCGGGGGCCGTG4140     GAGGTGCTGGGGGCGGAGGCGGGCTTGGCCACGCCCCCGCGGCGGGAAGTTGTGGACTGG4200     GAAGGCGCCTGGGACGAAGACGACGGCGGCGCGTTCGAGGGGGACGGGGTGCTGTAA4257     (2) INFORMATION FOR SEQ ID NO:2:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 1298 amino acids     (B) TYPE: amino acid     (C) STRANDEDNESS:     (D) TOPOLOGY: linear     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:     MetAlaSerGluAsnLysGlnArgProGlySerProGlyProThrAsp     151015     GlyProProProThrProSerProAspArgAspGluArgGlyAlaLeu     202530     GlyTrpGlyAlaGluThrGluGluGlyGlyAspAspProAspHisAsp     354045     ProAspHisProHisAspLeuAspAspAlaArgArgAspGlyArgAla     505560     ProAlaAlaGlyThrAspAlaGlyGluAspAlaGlyAspAlaValSer     65707580     ProArgGlnLeuAlaLeuLeuAlaSerMetValGluGluAlaValArg     859095     ThrIleProThrProAspProAlaAlaSerProProArgThrProAla     100105110     PheArgAlaAspAspAspAspGlyAspGluTyrAspAspAlaAlaAsp     115120125     AlaAlaGlyAspArgAlaProAlaArgGlyArgGluArgGluAlaPro     130135140     LeuArgGlyAlaTyrProAspProThrAspArgLeuSerProArgPro     145150155160     ProAlaGlnProProArgArgArgArgHisGlyArgTrpArgProSer     165170175     AlaSerSerThrSerSerAspSerGlySerSerSerSerSerSerAla     180185190     SerSerSerSerSerSerSerAspGluAspGluAspAspAspGlyAsn     195200205     AspAlaAlaAspHisAlaArgGluAlaArgAlaValGlyArgGlyPro     210215220     SerSerAlaAlaProAlaAlaProGlyArgThrProProProProGly     225230235240     ProProProLeuSerGluAlaAlaProLysProArgAlaAlaAlaArg     245250255     ThrProAlaAlaSerAlaGlyArgIleGluArgArgArgAlaArgAla     260265270     AlaValAlaGlyArgAspAlaThrGlyArgPheThrAlaGlyGlnPro     275280285     ArgArgValGluLeuAspAlaAspAlaThrSerGlyAlaPheTyrAla     290295300     ArgTyrArgAspGlyTyrValSerGlyGluProTrpProGlyAlaGly     305310315320     ProProProProGlyArgValLeuTyrGlyGlyLeuGlyAspSerArg     325330335     ProGlyLeuTrpGlyAlaProGluAlaGluGluAlaArgArgArgPhe     340345350     GluAlaSerGlyAlaProAlaAlaValTrpAlaProGluLeuGlyAsp     355360365     AlaAlaGlnGlnTyrAlaLeuIleThrArgLeuLeuTyrThrProAsp     370375380     AlaGluAlaMetGlyTrpLeuGlnAsnProArgValValProGlyAsp     385390395400     ValAlaLeuAspGlnAlaCysPheArgIleSerGlyAlaAlaArgAsn     405410415     SerSerSerPheIleThrGlySerValAlaArgAlaValProHisLeu     420425430     GlyTyrAlaMetAlaAlaGlyArgPheGlyTrpGlyLeuAlaHisAla     435440445     AlaAlaAlaValAlaMetSerArgArgTyrAspArgAlaGlnLysGly     450455460     PheLeuLeuThrSerLeuArgArgAlaTyrAlaProLeuLeuAlaArg     465470475480     GluAsnAlaAlaLeuThrGlyAlaAlaGlySerProGlyAlaGlyAla     485490495     AspAspGluGlyValAlaAlaValAlaAlaAlaAlaProGlyGluArg     500505510     AlaValProAlaGlyTyrGlyAlaAlaGlyIleLeuAlaAlaLeuGly     515520525     ArgLeuSerAlaAlaProAlaSerProAlaGlyGlyAspAspProAsp     530535540     AlaAlaArgHisAlaAspAlaAspAspAspAlaGlyArgArgAlaGln     545550555560     AlaGlyArgValAlaValGluCysLeuAlaAlaCysArgGlyIleLeu     565570575     GluAlaLeuAlaGluGlyPheAspGlyAspLeuAlaAlaValProGly     580585590     LeuAlaGlyAlaArgProAlaSerProProArgProGluGlyProAla     595600605     GlyProAlaSerProProProProHisAlaAspAlaProArgLeuArg     610615620     AlaTrpLeuArgGluLeuArgPheValArgAspAlaLeuValLeuMet     625630635640     ArgLeuArgGlyAspLeuArgValAlaGlyGlySerGluAlaAlaVal     645650655     AlaAlaValArgAlaValSerLeuValAlaGlyAlaLeuGlyProAla     660665670     LeuProArgAspProArgLeuProSerSerAlaAlaAlaAlaAlaAla     675680685     AspLeuLeuPheAspAsnGlnSerLeuArgProLeuLeuAlaAlaAla     690695700     AlaSerAlaProAspAlaAlaAspAlaLeuAlaAlaAlaAlaAlaSer     705710715720     AlaAlaProArgGluGlyArgLysArgLysSerProGlyProAlaArg     725730735     ProProGlyGlyGlyGlyProArgProProLysThrLysLysSerGly     740745750     AlaAspAlaProGlySerAspAlaArgAlaProLeuProAlaProAla     755760765     ProProSerThrProProGlyProGluProAlaProAlaGlnProAla     770775780     AlaProArgAlaAlaAlaAlaGlnAlaArgProArgProValAlaVal     785790795800     SerArgArgProAlaGluGlyProAspProLeuGlyGlyTrpArgArg     805810815     GlnProProGlyProSerHisThrAlaAlaProAlaAlaAlaAlaLeu     820825830     GluAlaTyrCysSerProArgAlaValAlaGluLeuThrAspHisPro     835840845     LeuPheProValProTrpArgProAlaLeuMetPheAspProArgAla     850855860     LeuAlaSerIleAlaAlaArgCysAlaGlyProAlaProAlaAlaGln     865870875880     AlaAlaCysGlyGlyGlyAspAspAspAspAsnProHisProHisGly     885890895     AlaAlaGlyGlyArgLeuPheGlyProLeuArgAlaSerGlyProLeu     900905910     ArgArgMetAlaAlaTrpMetArgGlnIleProAspProGluAspVal     915920925     ArgValValValLeuTyrSerProLeuProGlyGluAspLeuAlaGly     930935940     GlyGlyAlaSerGlyGlyProProGluTrpSerAlaGluArgGlyGly     945950955960     LeuSerCysLeuLeuAlaAlaLeuAlaAsnArgLeuCysGlyProAsp     965970975     ThrAlaAlaTrpAlaGlyAsnTrpThrGlyAlaProAspValSerAla     980985990     LeuGlyAlaGlnGlyValLeuLeuLeuSerThrArgAspLeuAlaPhe     99510001005     AlaGlyAlaValGluPheLeuGlyLeuLeuAlaSerAlaGlyAspArg     101010151020     ArgLeuIleValValAsnThrValArgAlaCysAspTrpProAlaAsp     1025103010351040     GlyProAlaValSerArgGlnHisAlaTyrLeuAlaCysGluLeuLeu     104510501055     ProAlaValGlnCysAlaValArgTrpProAlaAlaArgAspLeuArg     106010651070     ArgThrValLeuAlaSerGlyArgValPheGlyProGlyValPheAla     107510801085     ArgValGluAlaAlaHisAlaArgLeuTyrProAspAlaProProLeu     109010951100     ArgLeuCysArgGlyGlyAsnValArgTyrArgValArgThrArgPhe     1105111011151120     GlyProAspThrProValProMetSerProArgGluTyrArgArgAla     112511301135     ValLeuProAlaLeuAspGlyArgAlaAlaAlaSerGlyThrThrAsp     114011451150     AlaMetAlaProGlyAlaProAspPheCysGluGluGluAlaHisSer     115511601165     HisAlaAlaCysAlaArgTrpGlyLeuGlyAlaProLeuArgProVal     117011751180     TyrValAlaLeuGlyArgGluAlaValArgAlaGlyProAlaArgTrp     1185119011951200     ArgGlyProArgArgAspPheCysAlaArgAlaLeuLeuGluProAsp     120512101215     AspAspAlaProProLeuValLeuArgGlyAspAspAspGlyProGly     122012251230     AlaLeuProProAlaProProGlyIleArgTrpAlaSerAlaThrGly     123512401245     ArgSerGlyThrValLeuAlaAlaAlaGlyAlaValGluValLeuGly     125012551260     AlaGluAlaGlyLeuAlaThrProProArgArgGluValValAspTrp     1265127012751280     GluGlyAlaTrpAspGluAspAspGlyGlyAlaPheGluGlyAspGly     128512901295     ValLeu     __________________________________________________________________________ 

What is claimed is:
 1. A screening method for compounds having inhibitory activity against HSV ICP4 polypeptide-induced inhibition of apoptosis comprising the steps of:(a) providing a first cell comprising an HSV α4 gene under the control of an HSV immediate early promoter; (b) infecting said first cell with a herpes simplex virus that lacks a functional α4 gene; (c) contacting said first cell with a test compound; (d) incubating said first cell under conditions permitting viral replication; and (e) comparing the cell pathology of said first cell following incubation with (i) the cell pathology of a second cell that lacks an HSV α4 gene following infection with said herpes simplex virus and (ii) the cell pathology of a third cell comprising an HSV α4 gene under the control of an HSV immediate early promoter following infection with said herpes simplex virus but in the absence of said test compound.
 2. The method of claim 1, wherein said cell pathology comprises condensation of chromatin, obliteration of nuclear membranes, vacuolization, cytoplasmic blebbing and DNA fragmentation.
 3. The method of claim 1, wherein said first cell contains a wild-type HSV α4 gene under the control of an α4 promoter integrated into the genome of said first cell.
 4. The method of claim 3, wherein said herpes simplex virus that lacks a functional HSV α4 gene has a deletion in both copies of the virally-encoded α4 genes.
 5. A screening method for compounds having inhibitory activity against HSV ICP4 polypeptide-induced inhibition of apoptosis comprising the steps of:(a) providing a first cell comprising an HSV α4 gene under the control of an HSV immediate early promoter; (b) infecting said first cell with a herpes simplex virus that contains a conditionally defective α4 gene; (c) contacting said first cell with a test compound; (d) incubating said first cell under conditions permitting viral replication but resulting in the production of defective α4 gene product; and (e) comparing the cell pathology of said first cell following incubation with (i) the cell pathology of a second cell that lacks an HSV α4 gene following infection with said herpes simplex virus and (ii) the cell pathology of a third cell comprising an HSV α4 gene under the control of an HSV immediate early promoter following infection with said herpes simplex virus but in the absence of said test compound.
 6. The method of claim 5, wherein said herpes simplex virus that lacks a functional HSV α4 gene carries a temperature sensitive mutation in both copies of the virally-encoded α4 gene and the incubation is at 39.5° C.
 7. The method of claim 5, wherein said cell pathology comprises condensation of chromatin, obliteration of nuclear membranes, vacuolization, cytoplasmic blebbing and DNA fragmentation.
 8. The method of claim 5, wherein said first cell contains a wild-type HSV α4 gene under the control of an α4 promoter integrated into the genome of said first cell. 